Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/98

VARIATION reservation as to the possible creation of primeval forms and with Wallace s final caveat as to the origin of man, a thoroughly " monistic " view of biology and its kindred sciences is obtained. The systematic exclusion of the tra ditional teleology and of that operation of the consciousness of the organism assumed by Lamarck (since indefinite struc tural variations cannot be associated with, much less de veloped by, definite psychical ones, and still less by any per manent psychical bias or character) also necessarily follows ; and along with this goes the conception of the operation of an extra-organismal mind. The struggle for existence is the sole condition of human progress ; and the conception of prevalent or predominant altruism, as systematized by past philosophy and tradition, is thus an alloy of senti mental illusion with baser elements. The doctrine of natural selection is in this way fully developed into a substantially Neo-Lucretian philosophy, and, in justice to the logical clearness of the author to whom we especially owe this systematization, it must be admitted that those who grant his postulates, without endorsing his conclusions, have in all cases either refrained from continuing their development or fallen back upon the insertion of some caveat or deus ex machina at an arbitrary point. To In the same way we have this view of all things in organic s t ru ggl e applied to the explanation of the internal structure aml and function of the organism itself. Once more to quote function. Huxley, 1 " It is a probable hypothesis that what the world is to organisms in general each organism is to the mole cules of which it is. composed. Multitudes of these, having diverse tendencies, are competing with one another for opportunity to exist and multiply, and the organism as a whole is as much the product of the molecules which are victorious as the fauna or flora of a country is the product of the victorious organic beings in it." This view has more recently been considerably developed by Roux, 2 and from its logical continuity with the major theory of which it is a corollary is gaining widened acceptance. With regard to the destructive criticism of the old teleo logy, which has been led by Haeckel, and aided or ac quiesced in by other natural selectionists, it is important to note that the obvious proposition has also repeatedly been urged (e.g., by Huxley and Weismann no less than by their critics, such as Von Hartmann and Lotze), that, just in proportion as our explanation of the origin of organic structures, functions, and adaptations becomes in creasingly mechanical, so does an increasingly rigorous teleological view of this mechanism reappear. At most, therefore, we should have exchanged an external and mechanical view of teleology for an (at least relatively) internal and dynamical one. Sexual The later hypotheses accessory to natural selection can here be selection, only very briefly outlined. Partly in course of his inquiries into the descent of man, partly also to account for many remarkable phenomena of sexual differentiation in animals (see SEX), Danvin was led to develop the hypothesis of sexual selection which he had already suggested in the Origin of Species. Not merely do indi viduals struggle for existence, but the males struggle for the females ; thus the more vigorous tend to obtain mates, and so leave most progeny to repeat the struggle. Special weapons are used in the struggle, both offensive, like the cock s spurs or the stag s horns, and defensive, like the lion s mane ; and advantageous variations of these tend to be accumulated. But, as the more beautiful or melodious males appear often to obtain the preference of the females, there is also ground for the conception that the (esthetic advantages frequent in the male sex have similarly been acquired, the more so as we have common experience of how rapidly artificial selection can accumulate superiorities of plumage or song. After the opera tion of sexual selection has been traced as far as possible through the animal kingdom, the doctrine is applied to man, with the con clusion " that of all the causes which have led to the differences in 1 A frank and uncompromising application of this doctrine to the interpretation of nature and society will also be found in Huxley s "Struggle for Existence," in Nineteenth Century, February 1888. - Dcr Kampf d. Tlieile i>n Oryanismi s, Leipsio, 1876. external appearance between the races of man, and to a certain extent between man and the lower animals, sexual selection had been the most efficient." Acceptance of this hypothesis has been much less general than of natural selection. Criticism has been busy, and this ranges from the serious yet partial dissent of Wallace to fundamental contrast, such as is involved in the theory of the nature and origin of sex suggested in the article SEX, which views the degree of development of the external characters of sex as essen tially the outward expression of a proportional stage of the evolu tion of constitutional "maleness" or " femaleiiess " (i.e., katabolic and anabolic diathesis respectively). Under the title of " physiological selection " G. J. Romanes has rhysio- lately proposed " an additional suggestion as to the origin of species," logical of which the more critical than constructive essence may be briefly selection given in the author s own words : "As a theory of origin of species natural selection has in its way three cardinal difficulties, (1) the difference between species and varieties in respect of mutual fertility, (2) the swamping effects of free intercrossing upon an individual variation, (3) the inutility to species of so large a proportion of specific distinctions. . . . Natural selection is not, properly speak ing, a theory of the origin of species : it is a theory of the origin or rather of the cumulative development of adaptations. When ever any variation in the highly variable reproductive system occurs, tending to sterility with the parent form, without entailing fertility with the varietal form, a physiological barrier must inter pose, dividing the species into two parts, free to develop distinct histories, without mutual intercrossing, or by independent varia tion. By regarding mutually sterile species as records of variation in reproductive systems, we are at work, so to speak, on the foun dation of the matter." 3 LAWS OF VARIATION. Even those who attach most importance to the doctrine Origin oi of natural selection as affording a rationale of the process varia- of organic evolution will not seriously dispute that, even tlons< were this explanation completely extended to all the de tails of plant and animal life, another and deeper explana tion would still be necessary. That is, the theory of natural selection, being from the external standpoint only that of the adaptation of the organism to survive the pressures of the environment would all the more urgently stand in need of a complementary internal explanation, which should elucidate the physiological process of change through which the organism has actually been enabled to adapt itself. As a recent writer tersely expresses it, " The survival of variations is a matter secondary to their origin, and it is becoming realized more and more that this is the point to be explained." How, in short, do we get the variations without which natural selection would have nothing on which to operate 1 Here we can no longer Darwin s remain satisfied with the merely general conception of theory. . variation as essentially indefinite, with which we have be come familiar as the postulate (p. 81) of the theory of natural selection, 4 but must add to it a retrospect of the theories of earlier authors such as has been already out lined, (a) a summary and discussion of the extensive labours of Darwin upon the problems of variation from which this conception of indefiniteness was generalized, followed by (6) an account of subsequent progress. Un fortunately the voluminousness of this literature makes such a task practically impossible : instead of the enormous wealth of concrete details accumulated with respect to the Variation of Animals and Plants under Domestication, a reference to the volumes under that title must almost suffice. Some acquaintance with this work is, of course, necessary adequately to appreciate the force of its author s general con clusions ; these may, however, be briefly outlined from the chapter of the Origin of Species (chap, v.) devoted to the laws of variation, and from those (xxii.-xxvi.) of the larger work which contain an ample yet similar discussion. "Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we pretend to assign any reason why this or that part has varied. " Changed conditions generally Environ- induce mere fluctuating variability in individuals, yet sometimes ment. 3 Journ. Linn. Soc., xix., 1886. For the criticisms of Wallace, Argyll, Meldola, Catchpool, and others, see Nature, vol. xxxiv.

4 Coinp. Variation under Domestication, chap. xxi. , conclusion.